In general, a vehicle interior panel is formed by joining an inner case to an outer panel using vibration welding. The inner case has an opening for deploying an airbag and a flap portion formed together with a hinge portion in the opening. The outer panel covers the surface of the inner case and includes a door portion to be joined to the flap portion. One of joint surfaces between the flap portion and the door portion has a plurality of first welding ribs disposed substantially parallel to the hinge portion, a plurality of second welding ribs disposed so as to form a plurality of grids together with the first welding ribs, and a third welding rib formed in a frame shape thereon along the outer periphery of the door portion. By urging the first to third welding ribs against the back surface of the outer panel and vibrating the first to third welding ribs, the outer panel is welded and fixed to the inner case.
However, when the outer panel is vibration-welded to the inner case, the following problem arises. That is, the air in the grids formed by the first and second welding ribs is trapped in the grids and forms an air gap. Thus, jointing of the first and second welding ribs to the outer panel is interfered with the air gap and, therefore, the weld strength is decreased.
To solve such a problem, a vehicle interior panel with a surface skin (refer to, for example, Japanese Patent No. 4371780) has been proposed. A vehicle interior panel with a surface skin described in Japanese Patent No. 4371780 includes a base member (an outer panel), a surface skin bonded to a front surface of the base member, and a plastic structural member (an inner case) vibration-welded to the back surface of the base member. The base member has a through-hole for discharging air through a gap between the base member and the skin surface towards the back surface of the base member when the skin surface is bonded. One of the base member and the structural member has a welding rib formed thereon. The grid-shaped welding rib protrudes from one of the base member and the structural member towards the other and is vibration-welded. The welding rib has a communication channel allowing the through-hole to communicate with the outside. By using such a structure, when vibration welding is performed, the air in the grid is discharged outside through the communication channel. In this way, a decrease in the weld strength between the plastic structural member and the base member can be prevented.